Systems for converting an image or other optically detectable surface condition, such as characters on a document, into electrical signals which can either be stored in memory for later recall or which can be transmitted to a remote location over, for example, telephone communication lines or similar systems, are well know in the reproduction art. Systems of this type have generally been referred to as line scanners. In one type of line scanner, the image bearing document is held stationary and a photosensor or an array of photosensors is scanned across each line of the document along with a localized light source. In another type of scanner, the array of photosensors and light source are held stationary and the image bearing document is moved therepast. In both types of image scanning systems, as the document is scanned, the high optical density or dark portions of the document reflect less light from the light source for reception by the photosensors than the low optical density or light portions. As a result, the high and low optical density portions can be contrasted by the photosensors for photogenerating electrical signals representative of the image on or other surface characteristic of the document.
While systems of the type described above have been generally successful in fulfilling their intended purposes and have found commercial acceptance these systems have exhibited several deficiencies. One major deficiency heretofore encountered in devices of this type has been the need either for a lens array to focus the reflected light onto the sensing element, or to locate the image bearing surface in extremely close relationship to the photosensitive elements operatively disposed to scan the image on that surface. This close relationship between the image on the image bearing surface and the photosensitive elements was required in order to facilitate the "proximate focusing" of light from a small area portion of the image onto a corresponding small area photosensitive element. Due to the fact that that light quickly diffuses, if the photosensitive elements are not located in close proximity to said small area portions of the image upon the image bearing surface, light emanating from one small area portion thereof will diffuse onto photosensitive elements not corresponding to said small area portion. The result is the photogeneration of false signals by said small area photosensitive elements, which false signals provide a replicated image of poor resolution and quality.
Heretofore, this necessity for maintaining a close physical relationship between said elements and said image bearing surface could only be satisfied by having said photosensitive elements and an overcoat layer disposed thereupon actually slidingly engage and slide across the image bearing surface, which motion between the image bearing surface and the array of photosensitive elements resulted in a second deficiency of prior art imaging systems; i.e., said deficiency being the build-up of a large static charge on the image bearing surface. Therefore, such prior systems required that precautions be taken to prevent that static charge on said image bearing surface from inducing an electrical charge in the spacedly positioned array of photosensitive elements, which induced charge would be capable of deleteriously affecting and possibly fatally damaging said photosensitive elements. Previous attempts to solve this problem have focused upon the use of a static shielding layer interposed between the image bearing surface and the array of photosensitive elements. While this approach has proven successful in eliminating the deleterious effects of the static charge, it has also served to lengthen the distance between the image bearing member and the photosensitive elements, thereby reducing the quality and resolution of the image being generated by the photosensitive elements.
Previous attempts to employ fiber optic bundles as deposition substrates upon which photodetectors may be deposited have failed due to the rough uneven nature of said bundles. Thus, workers in the field were reduced to depositing the photosensitive elements upon separate substrates, which were subsequently suspended above said bundles. The result being greater processing expense and substantially inferior optical resolution.
The invention disclosed herein solves both the problem of maintaining said photosensitive elements in close proximity to said image bearing surface as well as the problem of static build-up discussed hereinabove. The present invention includes a thick dielectric material which provides sufficient electrical isolation between the photosensitive elements of the array and the static electrical charge built up on the image bearing surface being scanned that said static charge cannot harm the spacedly positioned photosensitive elements. Additionally, the present invention transmits radiation emanating from small area portions of the image on said image bearing document to corresponding small area photosensitive elements with such high resolution and efficiency in transmission so as to effectively approximate the presence of a zero thickness window between the image bearing surface and the array of photosensitive elements. Therefore, in the practice of the invention disclosed herein, it is only necessary that a light piping mechanism be placed in sufficient proximity to the image bearing surface to accurately transmit radiation from said small area portions of that surface. Because small area portions of the light piping mechanism receive radiation from only corresponding small area portion of said image and said mechanism is capable of transmitting radiation incident thereupon virtually without loss to corresponding small area photosensitive elements, said array of photosensitive elements need not be operatively disposed in close proximity to said image bearing surface.
These and other objects and dvantages of the subject invention will become apparent from the perusal of the Detailed Description Of The Invention, the Drawings and the claims which follow hereinafter.